Direction finding system



April 25, 1939.

G. w. PICKARD 2,155,838 DIRECTION FINDING SYSTEM Filed Oct. 18, 1935 30 INVENTOR. GREENLEAF W. PICKARD BY M gm ATTORNE Y.

Patented Apr. 25, 1939 UNETE STATES PATENT DIRECTION FINDING SYSTEM poration of Delaware Application October 18, 1935, Serial No. 45,538

4 Claims.

This invention relates to an improved direction finding system, and is particularly adapted to a directional aerial in which the tuning and control elements are remotely located from the aerial 5 or loop.

This invention is particularly adapted to highfrequency direction finding reception wherein it is desirable to reduce the high-frequency losses in the conductors to a minimum.

6 The principle upon which this invention is based is the employment of a comparatively long transmission line, and while it is well known in the prior art that long transmission lines, such as those employing concentric conductors, effi- 5 ciently transmit high-frequency currents at relatively great distances, in so far as I am aware,

such a system has not been adapted to direction finder use. Furthermore, it is an object of my invention to efiiciently couple the loop and the tuning elements with a long transmission line.

For successful operation of a direction finder, particularly when used in a high-frequency circuit, it is necessary that the transmission line be so coupled to the aerial that it does not in any way unbalance the aerial or loop, neither must the transmission line pick up any substantial amount of wave energy. Furthermore, the direction finder loop or aerial must have some form of index by which the position of the aerial is indi- 30 cated at the receiver position. Likewise, the aerial must rotate by a suitable motor located at the aerial, in which case the mechanical connection merely operates some form of indicator, or there is provided a mechanical linkage through 3 which the aerial may be rotated manually from the point where the receiver is located.

This invention will be best understood by referring to the accompanying drawing, in which Fig. 1 shows a diagram of a long transmission line coupled with a remotely controlled receiver;

Fig. 2 is a diagram of another modification of this invention, wherein the loop coupling comprises a push-pull amplifier;

Fig. 3 is a diagram of still another coupling ar- 45 rangement of the loop with completely shielded coupling elements.

Referring now in detail to Fig. l of the drawing, the directional aerial is indicated as I, which may be in any conventional form, such as a 50 rotatable loop or an Adcock directional aerial system; 2 is an electrically long transmission line; 3 indicates a coupling transformer having primary and secondary coupling coils 4 and 5 which have interposed an electrostatic shield 6 which is 55 connected to ground at 1. At the receiving end of the long transmission line there is located a second coupling unit which comprises coupling coils 8 and S which are electrostatically shielded by means of shield Hi. The secondary 9 of the coupling unit is connected to a receiving device which may be in the form of any conventional amplifying receiver ll, preferably of the short wave type. l2 indicates a mechanical connection to the loop which may be in any suitable form such as a flexible shaft which is remotely oper- 1O ated at a point l3 adjacent the receiver amplifier, or may be in the form of a motor which automatically and continuously rotates the loop, or in another form may be a mechanical linkage provided with a rotatable. shaft.

In Fig. 2, the aerial l is electrically coupled to the long transmission line 2 by means of a pushpull amplifier l5 which serves as a coupling unit, each side of the loop being symmetrically coupled to the primary coupling coil 4 by means of a pair of thermionic amplifier tubes l6 and N. This improved arrangement gives a symmetrical ecupling to the loop which will not unbalance the aerial I.

A further improvement which is particularly useful at the ultra high frequencies would be to provide a frequency converter stage at the loop so that the transmission line would be handling a much lower frequency than the signal wave. This may be accomplished by using an oscillator 30 I8 coupled to loop I by a coupling unit 2! and carried over line to a second coupling unit IS. The oscillator IB is arranged to beat with the signal frequency. The frequency of oscillator l8 will then beat with the loop signal producing a lower frequency to be transmitted over transmission line 2 to receiver H.

In the modification shown in Fig. 3, the entire coupling transmission line and receiving equipment are continuously shielded as indicated by dotted lines 25. Each of the coupling units is enclosed within separate shielded compartments 26 and 21, the loop being coupled by the coupling transformers 26 and 21. The transmission line is of low impedance shielded and substantially balanced. The shielded coupling transformer 21 is similar to coupling units shown in Figs. 1 and 2, except that the secondary is arranged with suitable terminals 29 and 30 for connecting coils of different electrical characteristics. For tuning 50 the entire loop circuit to resonance, there is arranged a tuning condenser 3|.

This invention covers both the tuned and untuned transformer and loop circuits.

In the tuned case, the loop may be wound to 55 the same inductance as would be required to cover the band if it were connected directly to the loop. Likewise, the transformers will be designed to represent the loop at the receiver end and will consist of probably fewer turns. The voltage gain, due to tuning of the loop, may equal as much as 50. When tuned directly at the loop without transformers, it might be 100.

In the case of an untuned transformer and loop, there would be required an increase in the number of turns on the loop. Also, the transformer would be overcoupled and have to be made broad enough to cover the entire band. Likewise, there would be no gain due to tuning since there is none. The transformers employed in the circuit may be either of the tuned or untuned type. The cores are made preferably of the powdered iron type, designed for tuning. likewise, transformers of the autotransformer type may be advantageously employed.

While only a few circuit arrangements of this invention have been described, it is distinctly understood that this invention may be arranged in any suitable manner .by those skilled in the art. Therefore, this invention should not be limited except as to such limitations as are clearly imposed by the appended claims.

Having thus described my invention, what I claim is:

1. A directional aerial, an electrically long transmission line having substantially no signal pickup, a push-pull radio-frequency amplifier for providing electrical symmetrical coupling means between said aerial and said transmission line, a receiver fed through said transmission line with signaling energy from said aerial, means including a mechanical connection between said aerial and a point located in the vicinity of said receiver for rotating said aerial, and an index controlled by the last said means.

2. A directional aerial, an electrically long transmission line having substantially no signal pickup, a push-pull amplifier and a frequencyconverter stage for providing electrical symmetrical coupling means between said aerial and said transmission line, a receiver fed through said transmission line with signaling energy from said aerial, means including a mechanical connection between said aerial and a point located in the vicinity of said receiver for rotating said aerial, and an index controlled by the last said means.

3. A directional aerial, an electrically long transmission line having substantially no signal pickup, a push-pull amplifier and a frequencyconverter stage for providing electrical symmetrical coupling means between said aerial and said transmission line, a receiver fed through said transmission line with signaling energy from said aerial, means including a mechanical connection between said aerial and a point located in the vicinity of said receiver for rotating said aerial, an index controlled by the last said means, and an oscillator electrically connected to said frequencyconverter.

4. A directional aerial, an electrically long transmission line having substantially no signal pickup, a radio frequency amplifier comprising a pair of tubes and a transformer having a powdered iron core for providing electrically symmetrical coupling means between said aerial and said transmission line, a receiver fed through said transmission line with signaling energy from said aerial, means including a mechanical connection between said aerial and a point located in the vicinity of said receiver for rotating said aerial, and an index controlled by the last said means.

GREENLEAF W. PICKARD. 

